Telephone device



Jan. 19 1926. 1,570,120

A. F. BENNETT.

TELEPHONE DEVICE Filed DSC. 6, 1923 @M Aff/1 Patented Jan. 19, 1926.

UNITED STATES 1,570,120. PAT-ENT OFFICE. I

ARTHUR F. BENNETT, F RICHMOND HILL. NEIN YORK, ASSIG-NOR. TO 'WESTERN' ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N. Y., A CORPORATION OF A NEW Yoan.

TELEPHONE DEVICE.

Applicationiled December 6, 1923. Serial No. 678,941.

To all whom. 'it may concern.'

Be it known that I, ARTHUR F. BENNETT, a citizen of the United States of America, residing at Richmond Hill, Long Island, in the county of Queens and State of New York, have invented certain new andvuseful Improvements in Telephone Devices, of

. which the following is a full, clear, concise,

. which -t marginal walls.

erated by the current through the comminuted material.

In its preferred embodiment2 the inven-v tion provides a micro hone device in which the rear wall of the c amber for the granular material, `is made of thin metal outwardly dished and has a lower thermal capacity and preferably a lower coeiii'cient "of expansion than the marginal walls soV that under the linitial heating of the com" minuted materiall it will move outwardly andas the marginal walls become heated and expand, it will caused to, move inwardly, thus maintaining a' ressure on the granular material -such'as will give the desired resistance. versus time characteristic.

Referring to the drawing: Fig. 1 is a longitudinal sectional yview o a micro hone embodying the invention in which t` e electrodes are disposed in opposite walls. v Fig. 2 isa longitudinal sectional view of a micro hone embodying the invention inv he electrodes are disposed inthe Fig. 3 shows curves illustrating the operation of the invention.

Referring particularly to Fig. 2, this invention is shown ap lied tov a transmitter of the type disclose in the` application of H. F. Dodge, Serial No. 525,898, filed December 30, 1921, which a small vibratory diaphragm loosely supported between'banks of paper rings. A-metal cu 7, the walls of which are partially line with asuitable insulating material 8r to insulate therefrom a circular plate 3, which is provided with an internally threaded flange v 4 at its periphery, and a stud 5, which may be used for mounting the device, extending through an aperture in the base of the cup 7. The plate 3 is provided with a depression 9 across'which is disposed a thin metal disk 18 shown dished slightl toward de ression 9 and secured in Iplace y means o an externally threaded annular electrode 6 engaging the flange 4f. Against the electrode 6 is disposed an annular insulating member or barrier 10l secured in place by a second annular electrode 12 having threaded engagement with the cup 7 which serves as a chamber. for the comminuted materialI 11 and the electrodes and V12. The cup 7 is provided with a diaphragm closure 13 loosely supported between banks of washers 16 and 17 and heldin place by means ofthe threaded ring 19, engaging the cup 7. A spacer ring 23 is provided between the electrode 12 andthe ring 19. This spacer Y ring is suiiiciently wide to prevent theL diaphragm 13 from being clamped between thewashers 16 and 17. y,

The operation of the invention may bev more readily 'understood by referring to Fig. 3, in which curve A represents the.

tightly due to the heating of the granular carbon and the marginal walls without the disk 18.

change in the resistance of the microphone 9b Curve Bfrejpresents the resistance `changes due to the heating of the compensating disk 18 of a material such as iron-or steel having` a lower coefficient of expansion thanv the marginal walls which are preferably of brass. Curve C represents the resultant and in this case the normal resistance o the micro hone. the case o curve A there is an initial negative change in the resistance. .This is due to thel fact that the resistance of the gran-- 'It will be noted .that in l ular carbon decreases-with its rise in temp perature and the carbon expands faster than the walls expand to relieve the pressure and increase the resistance. -,However,'as the walls gradually heat 'up and expand, the resistance change becomes ositivaas shown. .In the case of curve B t ere is increase 1n' the` ee. This is'due toI uol the outward bending of the compensating disk 18 which has a lower thermal capacity than the marginal walls and, therefore, heats up more. rapidly. This outward bending causes adecrease in the pressure on the carbon with a consequent increase in the resistance, but as the walls heat up, the disk 18 tends to flatten under the stretching action of the marginalwalls causing an increase in pressure with a corresponding decrease in resistance. By making the disk 18 completely compensate for the changes in the`resistance indicated by the curve A the normal resistance of the transmitter will remain substantially constant as shown by the curve C.

In some systemsfhowever, the initial resistance is of very short duration and relatively unimportant, whereas the nal resistance is a dominating factor. In this case it. may be desirable to have either a resultant decrease in resistance or a resultant increase in resistance and it is obvious from the curves that this may be accomplished by making the compensating disk 18 more or less responsive to the heat generated'in the granular material and controlling its d irection of operation. For example, if it 1s desirable to increase the transmitter resistance one way of accomplishing this 1s to reverse the compensating disc 18 so that it will bow toward the carbon granules thereby giving a resultant change in resistance -as illustrated by curve E, which is the resultant of the curve D representing the resistance change due to the disk 18 being reversed, and curve A. For the same disk curve D would be identical with curve A. By this arrangement the resistance may be made to increase to a very high value. Another way of increasing the transmitter resistance is to make the compensator 18 of a material having a higher coeflicient of eX- pansion and a lower thermal capacity than the marginal walls and dishing it away from the carbon granules as before.

Fig. 1 shows a well-known type of direct action microphone in which the disk 18 may also serve as one of the electrodes, in which case, the surface presented to the granular material is preferably gold plated. The other electrode is carried in the well known manner by a diaphragm 20 securely clamped between the cup 21 and the clamp.- ing ring 22. In order to insure that the diaphragm 20 will always be moved in the same direction it is provided with a corrugation, 25. With the corrugation 25 as shown the diaphragm 20 will tend to decrease the transmitter resistance and if reversed it will tend to make it breathe up.

The invention provides a convenient arrangement for positively controlling the action of a transmitter. With it the resistance of the transmitter may be kept within the value graphically represented in Fig. 3 by the curve C to any desired value by the proper selection ofthe material shape and dimensions for the disk 18 and dishing it in or out as desired.

What is claim is:

1. In a telephone transmitter, a container for comminuted material, a resilient member located within said container in contact with the comminuted material, and a mounting for said member adapted to change the shape of said member in response to the heat variations in said comminuted material.

2. In a microphone device, comminuted material, a metal container therefor, a concavo-conveX member mounted in the walls of said chamber and spaced from the rear wall and having its concave side incontact with the comminuted material, said' member having a lower coeiiicient of expansion than said container walls.

3. In a microphone device, comminuted material, a container therefor having a rear wall, a thin metal concavo-convex disc in said'container spaced from said rear wall, said disc having a lower coefficient of expansion than the Walls of the container and being of lower thermal capacity than said container walls.

4. A microphone device, comminuted material, a container therefor, a concavo-convex shaped member in said chamber adapted to modify its shape in response to the heat variations in said comminuted material to vary the pressure thereon.

5. In a microphone device, comminuted material and a container therefor, having a rigid outside and an inside resilient wall having its periphery secured to said rigid wall, said walls having different thermal capacities and adapted to control the pressure on said comminuted material in accordance with the heat variations in said material.

In witness whereof, I hereunto subscribe my name this 30th day of November A. D.,

ARTHUR F. BEN N ET'l. 

